Corrosion inhibitors



Allg.- 18, 1959 H. M. ZIMMERMAN ETAL 2,900,434

coRRosIoN INHIBITORS original Filed sept'. 15, 1955 INVENToRs HERMAN M. ZIMMERMAN ROBERT A. POWERS United States Patent CORROSION lNI-IIBITORS Herman M. Zimmerman, Lakewood, and Robert Powers, Cleveland, Ohio, assignors to Union Carbide Corporation, a corporation of New York Continuation of application Serial No. 541,856, September 15, `1955. This application January 3, 1956, Serial No. 557,013

11 Claims. (Cl. 13G- 161) This invention relates to corrosion inhibitors adapted for use in primary cells, particularly dry cells, and to cells containing such inhibitors.

Open circuit corrosion of dry cell anodes when the cells are on shelf or in storage or at rest during intermittent discharge is a problem which has troubled the dry cell industry from its inception. The unwanted consequences of this problem are perforation of the container anode, shortening of shelf life, and reduced service capacity. To cite but one example of its seriousness, in the case of telephone cells, approximately 50 percent as much zinc is removed from the anode by wasteful corrosion as by useful-current-producing, anodic attack.

To prevent or lessen such corrosion, many expedients have been suggested and tried, including the introduction in various ways of mercury, mercury salts and chromic salts in the cell.

Among the disadvantages of using mercury or mercury salts alone as cell corrosion inhibitors are the following:

(l) Zinc possesses metal impurities having low hydrogen overvoltage, which tend to accumulate on the anode surface during operation, with the net result that the overvoltage of the amalgam surface is lowered while the corrosion rate increases.

(2) The eifectiveness of amalgamation is limited by the extent to which air can be excluded from the cell.

(3) As corrosion is a surface reaction, only that mercury present at the anode-electrolyte interface is effective in reducing corrosion.

(4) Mercury must be uniformly distributed at the anode surface. Non-uniform amalgamation can arise in many- Ways in a dry cell, and lead to high corrosion rates.

(5) Because of its embrittling eifect on conventional anodic materials only very small amounts of mercury can be used. This is true regardless of Whether mercury or mercurio salts are employed.

Chromate inhibitors often prove unsatisfactory, as these are affected by the presence and nature of cell paste, and often lose their effectiveness during operation.

Previous Work using cationic organic compounds as dry cell corrosion inhibitors have shown them to be unsatisfactory in that they tend to form high resistance anode lms or react With cell components, although Wasteful anode corrosion may be low.

Lately it has been recognized that marked improvements in dry cell behavior with respect to corrosion inhibition can be obtained with inhibitors having several technical characteristics.

(l) Corrosion inhibiting materials should not react detrimentally with either electrolyte or cell mix.

(2) These should be of such form as always to be available at the anode in a proper concentration.

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(3) These should inhibit wasteful corrosion without reducing the anode eifectiveness.

In line with this realization and with a view to obviating prior art limitations, the principal object of the present invention is to provide corrosion inhibitors having novel and improved characteristics.

A further object of the invention is to provide a dry cell having substantially improved properties attributable to the incorporation therein of the corrosion inhibitors of the invention.

Seeking to attain these objects, We have discovered that non-ionic surface active compounds made by the addition of ethylenic oxide compounds to hydroxyl-bearing compounds effectively inhibit wasteful corrosion by raising the hydrogen overvoltage at the anode of the cells in which they are incorporated without adversely affecting normal cell performance.

In the drawings:

Fig. 1 is a sectional elevational View of a conventional paste-lined cell containing the compounds of the invention;

Fig. 2 is a sectional elevational View of a film-lined cell having the herein-disclosed additives;

Fig. 3 illustrates an external-cathode cell to which the corrosion inhibitors of this invention have been added; and

Fig. 4 is a sectional elevational View of a llat-type or stacked cell with the compounds of the invention.

The additioncompounds which successfully perform in Ithe practice of the invention' generally possess the formula R-O(R)--R", where R stands for alkyl, aryl or aryl alkyl radicals, Where R may be either hydrogen or a grouping similar to R, R is an alkoxy` radical such as ethoxy or propoXy, and n may be any number between l and 50. These compounds are essentially linear polymers having wetting characteristics. Their inhibiting properties result from high hydrogen overvoltage created on the anode surface.

Examples of the above compounds with their effect on hydrogen overvoltage are presented in Table I.

TABLE I Moles Relative Class of Starting Mate- Actual Starting Mate- Ethylene Overvoltrial rial Oxide age Added Polynuclear, Aromatic p-phenyl phenol 6 to 27 1.0 Phenols 2-naplithol 12 1.0 l-naphthol ll 1.0 Pheyl substituted Al- Triphenyl Methanol.- 14 0.5

co o s.

N onylpheno'l... 4 to 28 0.3 to 0.7 Alkylphenols Octylphenol. 4 to 40 Isooetylphen l0 Phenol Phenol 8 0.5 Z-ethyltllileXanoL (sgarter 13 0. 5 0D. el GI en 0 Allphatic Alcohols polyoxyethyleng chain). 2,6,8-trtmethyl-4 8 0. 2

Virtually all non-ionic `surfactants of this type can raise the hydrogen overvoltage. Maximum overvoltage effects result, however, from polyoxyethylated polynuclear aromatic phenols and alkyl aryl phenols. As little as 0.05 percent by weight of electrolyte or anodecontacting media of these materials suiice to satisfactorily prevent wasteful cell corrosion.

The corrosion inhibiting compounds of the invention may be incorporated in a cell by mixing with electrolyte or with the depolarizing mix, or in conjunction with the V16 intermediate the anode and cathode.

separator paste or film liner. Their effectiveness, however, is not affected Vby -the method of introduction, as long as they are rendered immediately available to the anode surface.

To provide an understanding of the invention, and for conciseness, it will be described mainly by illustrations of the performance of two compounds of the nonionic type. The rst of these, known as parahydroxydiphenyl polyethylene oxide, also is known as paraphenyl phenoxy polyethylene glycol, hereinafter is referred to as PPPG. This material is made by the addition of thirteen equivalents of Vethylene oxide to one equivalent of parahydroxydiphenyl. Its nominal structure is as follows:

`6, 13, 15, 18 or 27 equivalents of ethylene oxide).

(4) Polyglycol ether of triphenylmethanol (containing 14 equivalents of ethylene oxide).

(5) Polyglycol ethers of nonylphenyl (containing approximately 4, 6, 10, 11, 15, 30 or 40 equivalents of v ethylene oxide).

(6) Polyglycol ethers of octylphenol (containing approximately 3, 5, 7 or 9 equivalents of ethylene oxide).

(7) Polyglycol ether of phenol (containing 8 equivalents of ethylene oxide).

(8) Polyglycol ether of di(2ethyl hexanol) (containing 13 equivalents of ethylene oxide).

(9) Polyglycol ether of 2,6,8-trin1ethyl-4-nonyl (containing 8 equivalents of ethylene oxide).

10) Glycol ether of octylphenol (containing 1 equivalent of ethylene oxide).

(l1) polyalkyl ether of dodecylphenol (containing 75 Weight percent of mixed ethylene and propylene oxide).

Referring again to the general formula above, it is seen that R may `stand for the residue of an initially hydroxylic compound.

Fig. l represents a conventional dry cell having a container anode, preferably of zinc 10, an insoluble cathode, preferably of carbon 12, an electrolyte-Wet depolarizing mix consisting of manganese dioxide 14 and cereal paste The cereal paste, in this case, contains about 0.015 percent by Weight of p-phenyl phenoxy polyethylene glycol 18.

Fig. 2 is a conventional film-lined D-size round cell having aconsumable container anodeZl), preferably of zinc, an insoluble cathode 22, usually of carbon, an electrolyte-Wet depolarizing mix Z4 and an anode-contacting lm 26 intermediate the anode and cathode. In this case the lm has been modified by the incorporation therein of about 0.05 percent PPPG.

To incorporate PPPG in e D-size round cells, the standard procedure for making anode-contacting lilms was slightly modified. 0.75 gram of mercurio chloride and 2.3 grams of PPPG liquid were placed in hot, rapidly agitated, distilled water. To this stirred solution was added 9.52 grams of water-soluble 4000 c.p.s. methyl cellulose. .Stil-ring ywas continued until all the methyl )cellulose was wet. The resulting solution was then cooled I in an -ice bath with continued 4 A t stirring to maintain a uniform thickness, and until all the methyl cellulose dissolved. The solution was then poured on to a horizontal 300 square inch glass plate provided with a removable brim of plastic tape, and allowed to dry. The resulting film was about 0.0015 inch thick. A 21A inch by 4 inch portion of it was placed between the barrier layer and the zinc anode in several D-size cells. Table II below indicates a breakdown of solution and dried film composition and cell usage of anode iilms containing mercury and PPPG as combined zinc corrosion inhibitors for use in D-size cells.

TABLE I1 Film Identification Hg PPPG" fPPPG Control -l-Hg Solution Composition: Water g 600 600 600 4,000 c.p.s. water-soluble 9. 52 9. 52 9. 52 none 2. 30 2. 30 Mercurio chloride. r0. 75 none 0.75 Total grams soin/300 sq. in.

plate 610. 27 611. 82 612. 57 Film Composition/sq. in. Dry

Anode Film:

4,000 e.p.s. water-soluble methyl cellulose mg 31.75 31.75 31.75 PPPG 7. 65 7.65 Mercurio chloride 2. 50 2. 50

FILM USED PER D-SIZE CELL Total lm area per eel] 10.828 s in. Total film size per eell 2% x 4 s in. Total active nlm area/cell" 7.25 sq. in Total active film size/eell lm/ x 4 in Total lm thickness 0 0015 in Fig. 3 shows an external cathode cell comprising a non-corrodible tube 30, composed of brous material such as Wrapping paper, a cathode 32 of electrically conductive carbon composition molded in situ, an anode 34, preferably composed of zinc, centrally located in the cell, and provided with radial veins, and an electrolyte-wet depolarizing mix in the space intervening between the anode 34 and the cathode 32 at 36. The electrolyte in this instance contains about 0.05 percent by Weight of PPPG.

The at type battery of Fig. 4 comprises an outer container 40 containing a plurality of thin dry cells, lsuch as 42, composed of an electrolyte-Wet depolarizing mix 43, an anode-contacting lm y44, a zinc anode46 and a carbon cathode 48. The electrolyte has been modified in accordance with the method of the invention, by the addition thereto of 0.05 percent by Weight thereof of PPPG.

In the above cell, as in previous ones, the additive of the invention may be varied in accordance With the scope of the invention. Similarly the additives may be added singly, in mixtures thereof, with or without mercury inhibitors, to the depolarizing mix, or to the lm separator or liner. Again the quantity of additives may be modied Without departing from the scope of the invention.

Cells containing PPPG and mercury possess better current maintenance on 21 C. and 45 C. shelf life tests than do cells containing mercury alone. These data are presented in Tables III and IV for tests at 21 C. and 45 C., respectively, both for depolarizers consisting of electrolytic manganese dioxide and African ore (pyrolusite). As indicated in those tables, even after exposure to the severe storage conditions aiorded by a temperature of 45 C. and 50 percent relative humidity for 18 months, current maintenance values of over 60 percent for African ore and over 45 percent Afor-electrolytic manganese dioxide cells are obtained -with cells using the inhibitors of the invention.

TABLE III 1 Initial 12 Months 18 Months Example No. Depolarizer Inhibitor Zinc Cans Used Volts Amps. Volts Amps. CM 2 Volts Amps. OM 2 4 Electrolytic Manganese Hg Extruded high 1. 58 9. 3 1. 47 4. 2 45 1. 45 2. 2 24 Dio `de. purity Hg-l-PPPG do 1.59 7.9 1.42 5.1 65 1.49 4.6 58 Fre Soldered, alloy-- l. 58 8.9 1. 50 4. 7 53 1.48 3. 2 36 Hg-|-PPPG o 1. 59 7. 9 1. 50 4.8 61 1.48 4. 1 52 Hg Extruded high 1. 64 7. 5 1. 59 6. 3 84 1.58 6. 1 81 purity. Hg+PPPG do 1. 66 6. 4 1. 58 4. 9 77 1. 58 5. 5 86 Hg Soldered, alloy 1. 65 7.4 1. 59 5. 9 80 1. 58 5. 8 78 Hg-l-PPPG do 1. 60 6. 2 l. 58 4. 7 76 1. 56 4. 9 79 1 21 0. Shelf. 2 OM is used to designate current maintenance in percent.

TABLE IV 1 y Initial 12 Months 18 Months Example No. Depolarizer Inhibitor Zine Cans Used Volts Amps. Volts Amps. OM 2 Volts Amps. CM 2 Electrolytic Manganese Hg Extruded high 1. 57 9. 3 1. 46 2. 2 24 1.47 0.9 10

Dioxide. purity. do Y Hg+PPPG do 1. 58 7. 7 1. 49 3. 9 51 1. 49 3. 6 47 dn Ils Soldered, alloy.- l. 59 9. 4 1.48 4.1 44 1. 48 3. 4 36 do Hg-l-PPPG do l. 58 7. 7 1. 45 3. 6 47 1. 46 3. 5 45 African Ore Hg Extruded high 1. 65 7. 5 1. 57 5.0 67 1.56 2. 9 39 puri y. -.-do Hg+PPPG do 1. 65 6. 2 l. 57 4. 8 77 1. 57 4. 5 73 dn Hc Soldered alloy 1. 64 7. 3 1. 55 4. 7 64 1. 57 4. 6 63 do Hg+PPPG 1. 65 6. 2 1. 55 4. 4 71 1. 53 4. 2 68 1 -45 C. Shelf. 2 CM is used to designate current maintenance in percent.

Consideration of the data in Table III indicates that the inhibitors of this invention are particularly advantageously employed in soldered cell constructions where Imetal impurities and non-uniform amalgamation aggravates corrosion problems. Appreciable improvements in performance yare apparent also in the case of cells using the more highly active electrolytic manganese dioxide. In the past this depolarizer vadmittedly reduced shelf life.

All in all, the data above presented show a definite superiority in current maintenance for cells containing mercury `and PPPG over those containing mercury alone.

Results comparable with those discussed for iilm lined cells were obtained also With D-size paste-tilled cells, wherein eight and one-half milligrams of another effective agent, Neutronyx-600, per ten milliliters of paste have been added.

The disappearance of external indications of corrosion (perforation of zinc cans) `and the smoother surface of the lactive inside surface indicated that the inhibitor was extremely effective for reducing general zinc corrosion as well as eliminating areas of excessive corrosion up to ages of 24 months.

Initially the inhibitor reduces amperage, but the inhibited cells retain that :amperage to the extent that after 24 months storage at 21 C., 50 percent relative humidity, the inhibited cells exhibited a current maintenance TABLE V Service results 1 of mercury plus Neutronyx-O inhibited cells of 96 percent versus 74 percent for the control. This excellent amperage maintenance together with the high service level obtained after 12 months delay on intermittent =tests indicate that the inhibitor (Neutronyx-OO) is beneficial to the Leclanche cell.

TABLE VI Voltage and amperage maintenance for D-size inhibited round cells (mercury plus Neutronyx-600) (21 C.- 50% RH.)

-As for PPPG, the data presented above show a definite superiority in `capacity and current maintenance for cells containing both mercury and Neutronyx-GOO.

The experiments with Neutronyx-600 also otter evidence that the benets derived from non-ionics such as PPPG and Neutronyx does not reside mainly in their function as wetting agents.

The exact mechanism Iwhereby the desired eiects obtain is not known. The inter-action between PPlG and zinc aords a hypothesis. Taking electron diiraction patterns of an iabrafded zinc surface before 4and after contact with a 1 percent solution of PPPG in benzene, it Was observed that a definite amount of PPPG is rmly adsorbed by the zinc surface. The amount thus retained appears less than a full mono-layer, and is oriented with respect to the metal surface. This and other data indicate that PPPG is both chemically and physically adsorbed by zinc :and the observed increase in hydrogen overvoltage of zinc may be attributed to such an ,7 adsorbed layer. operation, our experiments highlighted in the present disclosurehave proven that the service life of cells is very materially increased for any service in which shelf life is :an `important factor.

The inhibitors of this invention find successful employment in various types of primary cell structures. Naturally, for best performance, optimum variations may be made from the `foregoing disclosure without departing from the spirit and scope of the instant invention.

rThis application is a continuation of our coi-pending application Serial No. 541,856, filed September l5, 1955.

What is claimed is:

l. In combination in a primary cell having a consum-V able anode, an insoluble cathode, an electrolyte-wet depolarizing mix, at least one corrosion inhibitor selected from the group consisting of mercury and mercury salts Y together with inhibiting means consisting of an organic corrosion inhibitor in contact with said consumable anode, said organic inhibitor being defined by the formula wherein R is initially a hydroxyl compound, R is an alkylene oxide radical selected from the group which consists of the ethoxy and propoxy radicals, and n is any number between 1 and 50, and R is at least one radical selected from the group which consists of hydrogen, alkyl, aryl and alkyl laryl radicals.

2. In combination in a primary cell having a consumable anode, an insoluble cathode, an electrolyte-wet depolarizer mix, corrosion inhibiting means consisting of at least one material selected from the group which consists of mercury andl mercury salts, and 'at least one organic corrosion inhibitor in contact with said consumable anode, said organic inhibitor being defined by the formula wherein R is initially a hydroxyl compound, R is an lalkoxy radical selectedv from the group which consists of the ethoxy and propoxy radicals, n is a number between 1 and 50, and R" is at least one radical selected from the group which consists of hydrogen, alkyl, aryl and alkyl aryl radicals.

3. In combination in a primary cell having a zinc anode, -a carbon cathode, ya depolarizer mix consisting of manganese dioxide and atleast one organic corrosion inhibitor in contact with said zinc anode, said organic inhibitor being defined Vby the formula wherein R is initially an alcohol, R' is an ethoxy radical and n :is a number between 1 Iand 50, and R" is at least one radical selected from the group which consists of hydrogen, alkyl, aryl and alkyl -aryl radicals, and an in,- organic inhibiting material selected from the group which consists of mercury and mercury salts.

4. In combination in a primary dry cell having a zinc anode, an electrolyte-wet mang-anese dioxide depolarizer mix, a carbon cathode and corrosion inhibiting means However, regardless of any theory of Y consisting of p-phenyl phenoxy polyethylene glycol and mercury.

In combination ina primary cell having a zinc anode, an insoluble cathode, `an electrolyte-wet depolarizing mix consisting of manganese dioxide, cereal' paste intermediate said anode and cathode, said cereal paste containing p-phenyl phenoxy polyethylene glycol and mercuryto inhibitwasteful corrosion of said zinc anode. Y 6. In combination in a primary cell having a zinc anode, a carbon cathode, a depolarizing mix consisting of V4manganese dioxide` and an electrolyte containing mercury l ful corrosion of said zinc anode.

7. In combination in a primary cell having a zinc Yan- A ode, a carbon cathode, afdepolarizing mix, an electrolyte containing at least one polyoxyethylated alkyl phenol and conventional mercuric inhibitors.

8. In combination in a primary galvanic cell having an electrolyte-wet depolarizing mix, a consumable anode, a cathode, -a film separator between anode land cathode, said film separator having at least about 0.05 percent by weight thereof of a polyoxyethylated polynuclear phenol and at least one corrosion inhibitor selected' from the group consisting of mercury and mercury salts.

9. Incombination in a primary galvanic cell having an electrolyte-wet depolarizing mix, a consumable anode, a cathode, a lm separator between anode and cathode, said film separator having at least about 0.05 percent by weight thereof of a polyoxyethylated phenol and at least one corrosion inhibitor selected from the group consisting of mercury and mercury salts.

10. In combination in a primary galvanic cell having an electrolyte-wet depolarizing mix, a consumable anode, a cathode, a film separator between anode and cathode, said iilm separator having at least about 0.05 percent by weight thereof of `an alkyl phenol polyglycol ether and at least one corrosion inhibitor selected from the group consisting of mercury and mercury salts.

1l. In combination -in a primary galvanic cell having an electrolyte-wet depolarizing mix, a consumable anode, a cathode, a film separator between anode and cathode, said film separator having about 0.05 percent by weight thereof of a p-phenyl phenoxy polyethylene glycol and mercury to inhibit the wasteful corrosion of said zinc anode.

References Cited in the tile of this patent UNITED STATES PATENTS 1,366,298 Teitelbaum Jan. 18, 1921 1,639,984 Brown Aug. 23, 1927 2,598,226 Coleman May 27, 1952. 2,619,437 Glasstone Nov. 25,' '.1952 2,624,706 Maxcy et al Ian. 6, 1953 2,630,380 Hanson et al. Mar. 3, 1953 2,677,700 Jackson et al May 4, 1954 2,748,183 Morehouse et al May 29, 1956 FOREIGN PATENTS 534,618 Great Britain Mar. 12, 1941 

1. IN COMBINATION IN A PRIMARY CELL HAVING A CONSUMABLE ANODE, AN INSOLUBLE CATHODE, AN ELECTROLYTE-WET DEPOLARIZING MIX, AT LEAST ONE CORROSIN INHIBITOR SELECTED FROM THE GROUP CONSISTING OF MERCURY AND MERCURY SALTS TOGETHER WITH INHIBITING MEANS CONSISTING OF AN ORGANIC CORROSION INHIBITOR IN CONTACT WITH SAID CONSUMABLE ANODE, SAID ORGANIC INHIBITOR BEING DEFINED BY THE FORMULA 